I have tried increasing and reducing the standoff disctance by 1 inch, but no improvement on the porosity.
I have tried increasing the chamber pressure to 108.9 psi by increasing the oxygen and the fuel flow, but no improvement on the porosity.
Standoff: 14"
Any one can give me some adivice on how to improve from 2% to less than 1%

Quote:Is there anyone has any idea how to differentiate pull out from porosity?

With porosity levels ~ 2 - 5% you should be able to infiltrate these with epoxy resin. Use vacuum impregnation (failing that put a few drops of epoxy resin on the warmed sample (~ 80 -100*C) and then quickly hot/pressure mount in bakelite. Works very well, but can gum up the mounting press if your not careful) on the samples before mounting and polishing, this allows you to detect true porosity when these sites are filled with epoxy. If samples show little impregnation, particularly near coating surface, then suspect pull-out. Usually, these coatings are too dense to allow any noticeable impregnation.

I don't think reducing the spray should do too much harm to coating quality, in fact it will probably improve it, but at the expense of production time and increased use of process gases/fuel.

Quote:If we reduce the powder spray rate and reduce the linear speed, will it increase the efficiency?

Reducing spray rate may increase deposit efficiency slightly. Changing speeds and feeds should really have little effect other than to cause problems with overheating if set too low. Process or economic efficiency on the other hand will suffer, with lower productivity and higher gas/energy consumption per job.

Quote:I am using powder 88%WC 12%Co (88% Tungsten carbide 12% Cobolt)

What is the specific make and grade? Is it optimised for this process?

I am not sure whether our lab is doing the correct ginding and polishing.
Because there are some differences between our own result and third party result, although the third party claim that theirs might have some smearing effects.
Is there any recomemded steps for polishing this powder?
Image Attached for third party inspection.

First, I hope you don't mind, but I have converted your original bmp image ~ 250KB to a JPG image ~ 11KB. Makes a big difference when considering server speed/bandwidth and memory

It not really possible to tell from your image whether this is smeared or not. The coating density/porosity level looks inline with what you would expect though. Just goes to show importance of interpretation and methods of metallography. Useful tool, but so easy to get wrong.

I think the most important step for your metallographic preparation would be epoxy impregnation of your samples to determine whether your apparent porosity is pull-out or real. If you get no impregnation, chances are that your real porosity level is below the !% mark. Polishing procedure - well the majority of my experience is with manual polishing, so metallographers experience and skill play a significant part as well as procedure. I use silk clothe for diamond polishing and a very short final polish on soft clothe with colloidal silica just to give a slight relief effect (viewing microstructure between steps to check progression).

The specific powder you are using for this job will have a big effect on the quality of coating. Are you using a praxair or similar powder optimised for this process or are you using an unknown possibly customer supplied or specified?

(09-18-2008 08:00 PM)Gordon Wrote: First, I hope you don't mind, but I have converted your original bmp image ~ 250KB to a JPG image ~ 11KB. Makes a big difference when considering server speed/bandwidth and memory

No Problem

(09-18-2008 08:00 PM)Gordon Wrote: I think the most important step for your metallographic preparation would be epoxy impregnation of your samples to determine whether your apparent porosity is pull-out or real. If you get no impregnation, chances are that your real porosity level is below the !% mark.

Thanks I will ask the lab engineer to try out.

(09-18-2008 08:00 PM)Gordon Wrote: Polishing procedure - well the majority of my experience is with manual polishing, so metallographers experience and skill play a significant part as well as procedure. I use silk clothe for diamond polishing and a very short final polish on soft clothe with colloidal silica just to give a slight relief effect (viewing microstructure between steps to check progression).

They are using some struers grinder to gind and polish. But the rotation speed, force and duration is standard to most coating. I think recently they just realized that the different in setting will contributes to different results.

(09-18-2008 08:00 PM)Gordon Wrote: The specific powder you are using for this job will have a big effect on the quality of coating. Are you using a praxair or similar powder optimised for this process or are you using an unknown possibly customer supplied or specified?

ya, we are using Praxair powder. Actually, I have a good support from Hs Stack although I am not using HS powders. Will think to switch from Praxair to HS.

(10-01-2008 11:52 AM)William Wrote: Hi all,
I have one question.
I don't know, how to set rotation rate of the polishing disk and fixed support(mount) on the automatic polisher.
Is rotation rate of the polishing disk same fixed support?

regards,

william

Don't think I can help too much, but I think it will be very dependant on your specific polishing equipment. Some will have fix disk rotation speed and head speeds/direction, while others have variable everything You will need to experiment to see which settings give the best results for your particular samples.

I have tried increasing and reducing the standoff disctance by 1 inch, but no improvement on the porosity.
I have tried increasing the chamber pressure to 108.9 psi by increasing the oxygen and the fuel flow, but no improvement on the porosity.
Standoff: 14"
Any one can give me some adivice on how to improve from 2% to less than 1%